Articles designed to resist ballistic impact, such as bulletproof vests, helmets, body armor, armor plate and other police and military equipment, structural members of helicopters, aircraft, ships, and vehicle panels and briefcases containing high strength fibers, are known. Known high strength fibers include aramid fibers, fibers such as poly(phenylenediamine terephthalamide), ultra-high-molecular-weight polyethylene, graphite fibers, ceramic fibers, nylon fibers, glass fibers and the like. The fibers are generally encapsulated or embedded in a continuous matrix material structure and, in some instances, are joined with rigid facing layers to form complex composite structures. Armor should provide protection against ballistic projectiles such as bullets and other like piercing objects or state of the art projectiles. However, body armor, bulletproof vests, etc. may be stiff and restrict the wearer's movement.
Ballistic-resistant composite articles have been disclosed in Harpell et al. U.S. Pat. Nos. 4,403,012; 4,501,856 and 4,563,392. These patents disclose networks of high strength fibers in matrices composed of olefin polymers and copolymers, unsaturated polyester resins, epoxy resins, and other resins curable below the melting point of the fiber. While such composites provide effective ballistic resistance, A. L. Lastnik et al.: “The Effect of Resin Concentration and Laminating Pressures on Kevlar Fabric Bonded with Modified Phenolic Resins”, Technical Report NATICK/TR-84/030, Jun. 8, 1984, has disclosed that an interstitial resin, which encapsulates and bonds the fibers of a fabric, reduces the ballistic resistance of the resultant composite article. Therefore, a need exists to improve the structure of composites to effectively utilize the properties of the high strength fibers.
U.S. Pat. No. 4,623,574, Harpell et al., filed Jan. 14, 1985, and commonly assigned, discloses simple composites comprising high strength fibers embedded in an elastomeric matrix. Surprisingly, the simple composite structure exhibits outstanding ballistic protection as compared to a simple composite utilizing rigid matrices, the results of which are disclosed therein. Particularly effective are simple composites employing ultra-high molecular weight polyethylene and polypropylene such as disclosed in U.S. Pat. No. 4,413,110.
Composites having continuous domains are disclosed in the art, generally restricting the percentage of resin to be at least 10 volume percent of the fiber content. U.S. Pat. No. 4,403,012 discloses a matrix in the preferred range of 10–50% by weight of fibers. U.S. Pat. No. 4,501,856 discloses preferred fiber network content of 40 to 85 volume percent of the composite. U.S. Pat. No. 4,563,392 does not disclose any range for amounts of a matrix component. It is desirable to maintain as high a volume and/or weight percent of fiber as possible within a resultant composite to enhance ballistic resistance.
U.S. Pat. Nos. 5,061,545 and 5,093,158, both commonly assigned, disclose a fiber/polymer composite with non-uniformly distributed polymer matrix, and a method of making the composite. These patents are directed to a fibrous web having a network of unidirectional fibers, and a matrix composition non-uniformly, but continuously, distributed in the major plane of the fibrous web. The fibrous web becomes encased in the matrix composition, and although non-uniformly distributed, the matrix composition remains as a continuum, attaching to all fiber members of the fibrous web. The patents disclose non-uniformly distributing polymeric composition together with a fibrous web so that there is a patterned surface, causing portions of the resultant combined web to have greater amounts of polymer than other portions. Thus, the total amount of polymer necessary to maintain the integrity of the polymer-impregnated web was reduced. The patents further disclosed that the thick areas which provide the integrity of the polymeric layer preferably provide a continuous area along the surface of the fibrous/polymeric composite.
Other patents, such as U.S. Pat. No. 4,623,574, have shown the difficulty in preparing a composite made of a fabric web within a polymeric matrix. In Table 6, sample 12, when a high amount of fiber was used, the sample lacked consolidation and could not be tested.
Cost and fabric quality also affect the availability of armor. Conventional fabric cost rises dramatically as yarn denier decreases. Additionally both ballistic performance and flexibility improve as the areal density of individual layers decreases.